It is common with conventional beds to have a number of semi-connected springs within a mattress. These systems tend to have two inefficiencies. Firstly, the springs are connected and are, therefore, not totally independent of each other. When a downward pressure is exerted upon one spring it exerts a downward pressure upon the adjoining springs to which it is connected. Secondly, each spring has the same load rating which inhibits effective response to all the various weights and contours of a human body.
Waterbeds attempt to solve these problems but introduce two other inefficiencies. Firstly, a "ballooning" of nonused areas of the bed occurs which creates a crater effect where the bulk of body weight is supported. This results in raised legs, head and arms. Secondly, when the membrane to contain the water is made with sufficient strength to avoid bursting or being pierced, it will not flex appropriately to mold itself to body contours.
Attempts have been made to construct beds with a plurality of vertically aligned body support members which communicate with a common fluid chamber. An example of such a bed is U.S. Pat. No. 5,210,889 which issued to Wesemann et al in 1993. This type of bed addresses a number of the described problems. A downward pressure upon one of the body support members does not effect adjoining body support members, and yet such downward pressure is transmitted via fluid in the fluid chamber equally amongst all body support members. The operation of the body support members and common fluid chamber accommodates a differential response to the various weights and contours of the human body. However, beds constructed in accordance with the teachings of Wesemann are still subject to a form of "ballooning" in which a lifting of the unloaded body support members occurs.